Hybrid powertrains utilize more than one power source to generate the torque and power needed to meet the demands of the application in which the hybrid powertrain is employed. A hybrid powertrain may include a first power source (e.g., an internal combustion engine) and a second power source (e.g., an electric motor/generator and associated battery pack). The powertrain further generally includes interfacing hardware, electronic controllers, linking networks, power electronics, an engine compartment, a vehicle body, a transmission, etc. To supply power effectively, a hybrid powertrain system requires a determination of the total torque and/or power requirement for the powered application, a determination of the contributions from the available power sources that will be provided to meet the total torque and/or power requirement, and finally control of the individual power sources to meet the determined individual contributions.
Controlling the contributions of the available power sources is complex and depends upon the application and demanded duty cycle of the hybrid powertrain. Common control schemes involve comparing efficiency of the internal combustion engine and efficiency of the electric motor/generator. Other methods include attempting to convert an electrical power quantity to an equivalent fuel quantity or to some other sort of cost function. Fundamentally, these methods employ efficiency maps of the internal combustion engine and the electric motor/generator. However, such efficiency maps can yield less than optimal results because each predicts low efficiency at low power levels. Accordingly, there remains a need for further contributions in this area of technology.